Seashell Technology has developed an assay that can optically detect single molecular events in real time. The assay makes use of the unique properties of the plasmon resonant particle (PRP), an extremely bright, non-bleaching, sub-micron reporter label. The measured release of individual PRPs from a solid substrate by cleavage of susceptible linker molecules is used as an ultrasensitive detector of enzymatic activity. We have designed and implemented two sensitive assays based on the PRP release format (1) a polypeptide linker that detects protease activity, and (2) a nucleic acid linker that detects restriction enzyme mediated cleavage. In addition, we have demonstrated that proteins that bind to the linker blocking the cleavage site, or bind directly to the enzyme, inhibiting the enzymatic activity, can be detected. The developed assays will be simple to use, require very small quantities of sample, and will be detectable in real time. We expect the results of our SBIR program, in collaboration with industrial partners, to allow us to create commercial products for sale to both the research and clinical biomedical communities.